1. Field of the Invention
This invention relates to a display device, and more particularly to a fluorescent display device having a plurality of control electrodes electrically separated from one after another for energizing different types of indicia.
2. Description of the Prior Arts
In a fluorescent display device formed of a substrate and a front cover which are airtightly sealed to form a vacuum envelope, control electrodes (hereinafter referred to as grids) are mounted on the substrate in such manners as shown in FIG. 1 (A) and FIG. 1 (B). In FIG. 1 (A), the grids 2 are directly bound on the substrate 3 by applying an adhesive material 1, such as, for example, crystalline powdered glass or the like, to the periphery of the grids 2 which are to be mounted on the substrate 3 in an opposed relationship to anodes (not shown) on which phosphor layers are deposited, and the subjecting the adhesive material 1 to heat at a high temperature for calcination and crystallization of the adhesive material 1. However, in the method of fixing grids by means of the adhesive material, it is difficult to determine exact locations for mounting the grids 2 with respect to the substrate 3, and a complicated bonding operation is required when the grids 2 are provided with a display device in which several kinds of display patterns are intricately incorporated. Furthermore, the phosphor layers deposited on the anodes are deteriorated by gas generated at the time of baking and crystallizing the adhesive material at the high temperature in order to fix the grids 2 to the substrate 3.
In view of the forgoing, it has been proposed and put into practical use to fix grids to a substrate as shown in FIG. 1 (B). In FIG. 1 (B), the grids 2 are fixed to spacer frames 4 having at least two leads 5 extending to the opposite directions at the upper and lower edges thereof, which are in turn held between a sealing portion of the substrate 6 and a front glass forming the outer envelope. This method is advantageous in that each of the grids 2 can be easily mounted at proper position of the substrate 6, and also the intermediate baking and crystallizing operation of the adhesive agent at the high temperature in order to fix the grids to the substrate which accompanies the generation of the hazardous gas can be entirely eliminated.
As a means for displaying various informations, there are a digital display system representing the informations in the form of numerals, an analog display system representing the informations in the form of graphs different in shape depending upon the magnitude of the input informations, and a graphic display system representing the informations in the form of figures. In the fluorescent display device, it is possible to effect the various types of the display as explained hereinabove, and the fluorescent display device can be formed in a composite structure capable of effecting the various types of the display, such as for example, both bar graphical and numerical displays, or time and program, in a single envelope. In order to effect the display of these complicated informations in the single envelope of the fluorescent display device, it is advantageous to divide the grid disposed between the anodes and cathodes into several pieces so as to electrically isolated each of the grids, and to actuate the fluorescent display device by a dynamic drive system.
However, when the composite fluorescent display device for effecting the display of the complicated multiple informations is constructed with the use of a plurality of the grids, the grids must be arranged in an extremely complicated manner. For example, in the method of mounting the grid by having the leads sandwitched at the sealing portion of the base substrate and the front glass as shown in FIG. 1 (B), it is impossible to provide the lead with at least some of the grids at their opposite ends thereof in view of the arrangement of the grids in the complicated manner within the tube. Thus, some of the grids are unstably held at their ends thereof in a cantilever fashion. When the unsealed ends of the grids are welded to the substrate by baking with the use of the adhesive material such as the crystalline powder glass as shown in FIG. 1 (A), it creates the same problems as explained hereinabove.